1. Field of the Invention
The present invention relates to an optical disc apparatus having a function of recording a signal on and reproducing a signal from a disc such as a compact disc (CD), a mini disc (MD) and a digital versatile disc (DVD), and particularly relates to an optical disc apparatus which is arranged to adjust by rotating a screw the inclination angle of an objective lens that scans the surface of the disc.
2. Description of the Related Art
A conventional optical disc apparatus will be described with reference to FIG. 6. The optical disc apparatus includes an optical pickup unit shown in FIG. 6. The optical pickup unit exemplarily shown in FIG. 6 is arranged in a manner that a lens holding member 2 attached with a hood-shaped cover 21 is mounted on a base body 1 provided with a rack 11 serving as an input portion for a driving force. In the lens holding member 2, the cover 21 is attached on a frame 22 fixed on the base body to adjust an inclination angle. The cover 21 surrounds the periphery of the lens holding member having an objective lens and held by the frame 22 (the lens holding member having the objective lens is not shown in FIG. 6). The base body 1 is provided with a guide hole 12 and a screw hole 4 at the both sides sandwiching the lens holding member disposing position A rod-shaped guide shaft 3 fits in the guide hole 12 in a relatively slidable and rotatable manner. An adjusting screw 106 is screwed into a screw hole 4. The adjusting screw 106 is provided with a concentric slidable portion 62 configured by an annular groove portion formed by a pair of flanges 61, 61. The slidable portion 62 fits with a rail portion 8 extending in parallel to the guide shaft 3 so that the slidable portion is slidable along the rail portion. The rail portion 8 is integrally formed with a not-shown chassis (drive chassis) formed by synthetic resin molding. The guide shaft 3 is attached to the chassis.
In the optical disc apparatus provided with the optical pickup unit shown in FIG. 6, when a driving force is applied to the optical pickup unit through the rack 11, the base body 1 on which the lens holding member 2 is mounted is guided along the guide shaft 3 and reciprocally moved along a disc surface D shown by an dashed line in the radial direction thereof. According to this moving operation, a laser beam passed through the objective lens is irradiated on the disc surface D.
In the optical pickup unit shown in FIG. 6, the frame 22 of the lens holding member 2 is fixed to the base body 1 after suitably adjusting the inclination angle of the objective lens of the lens holding member. When only such an adjustment of the inclination angle is performed, the posture of the base body 1 may vary depending on the variation of the relative positional relation between the rail portion 8 and the guide shaft 3 supporting the base body 1. Thus, the optical pickup unit is arranged in a manner that the inclination angle of the objective lens can also be adjusted by changing the posture of the base body 1. Such an adjustment of the inclination angle is performed by rotating the adjusting screw 106.
That is, since the height level of the slidable portion 62 fitting with the rail portion 8 is constant, when the adjusting screw 106 screwed into the screw hole 4 is rotated in a positive direction or a reverse direction, the base body 1 swings upward or downward with respect to the slidable portion 62 around the axis line of the guide shaft 3, whereby the posture of the base body 1 changes. As a result, the inclination angle of the objective lens of the lens holder provided in the lens holding member 2 is adjusted.
FIG. 5 is an enlarged diagram showing an engaged state between a main portion of the adjusting screw 106 employed in the conventional optical pickup unit and the screw hole 4 provided in the base body 1.
The size and the shape of a male screw 163 of the adjusting screw 106 and a female screw 41 of the screw hole 4 shown in this figure are conform to JIS standard. The male screw 163 is formed by a single spiral-shaped screw thread 164 extending smoothly and continuously, whilst the female screw 41 is formed by a single spiral-shaped valley-shaped groove 47 extending continuously. In a state where the male screw 163 is screwed into the female screw 41, a gap S is defined between the male screw 163 and the female screw 41 as shown in this figure. This gap S serves to improve the operability at the time of screwing the adjusting screw 106 into the screw hole 4. The adjusting screw 106 is integrally formed by synthetic resin together with the pair of flanges 61 shown in FIG. 6 and a tool engaging portion (not shown). The adjustment screw further includes a shaft portion 165 having a circular section which is adjacent to the forming portion of the male screw 163. When the male screw 163 is screwed into the female screw 41, the shaft portion 165 is fit into a no-thread hole portion 43 provided adjacent to the screw hole 4 in a manner that a slight gap 44 is defined therebetween.
JP-A-11-232653 (prior art 1) shows an example in which a convex portion provided with a sphere surface is formed on a lens attachment plate at which an objective lens is held, the convex portion is overlapped on a concave portion having a sphere surface of a base table, and bolts are inserted into through holes disposed at the both sides sandwiching the concave portion of the base table, respectively. These bolts are respectively screwed into the screw holes of the lens attachment plate and one of these bolts is urged downward by a compression spring thereby to attach the lens attachment plate to the base table. In this example, when one of the bolts inserted into the through holes is rotated, the convex portion slides with the concave portion to change the lens attachment portion thereby to adjust the inclination angle of the objective lens held by the lens attachment plate.
JP-A-9-21937 (prior art 2) relates to an optical element positioning fixing apparatus and describes that the position of a prism holder is adjusted in a state where the prism holder on which a prism serving as an optical element is mounted is provisionally fixed to a base member by means of a single fixing screw so as to be movable in the horizontal direction, and thereafter the prism is fixed to the base member by using plural fixing screws.
JP-A-2002-15434 (prior art 3) and JP-A-2002-15433 (prior art 4) disclose that the inclination angle of an objective lens of an optical pickup is adjusted by adjusting the inclination of a guide shaft for guiding the movement of the optical pickup of a disc apparatus, by using a spring member and an adjusting screw.
Each of the bolt of the prior art 1, the fixing screw of the prior art 2 and the adjusting screws of the prior art 3 and the prior art 4 is assumed to be arranged in a manner that a male screw having a single spiral-shaped thread extending smoothly and continuously is screwed into the female screw of a screw hole serving as a partner side screw.
As described with reference to FIG. 5, according to the conventional optical disc apparatus, each of the screw thread 164 of the male screw 163 of the adjusting screw 106 and the valley-shaped groove 47 of the female screw 41 of the screw hole 4 is extending smoothly and continuously. Since the gap S is defined between the male screw 163 and the female screw 41 engaged to each other, the adjusting screw 106 may be rotated unexpectedly. For example, at the time of moving the base body 1 in the disc radial direction, when the slidable portion 62 (see FIG. 6) disposed on the adjusting screw 106 rubs with the rail portion 8 of the chassis and so rotation moment is applied to the adjusting screw 106, the adjusting screw 106 rotates unexpectedly due to the rotation moment. Further, when various kinds of vibration is applied to the adjusting screw 106, the adjusting screw 106 also rotates unexpectedly due to the vibration. When the adjusting screw 106 rotates unexpectedly in this manner, the base body 1 swings upward or downward around the axis line of the guide shaft 3 by an amount corresponding to the rotation amount of the adjusting screw 106. Thus, there arises a phenomenon that the inclination angle of the objective lens deviates and so the recording or reproducing efficiency may be degraded due to such a deviation. In order to prevent such a phenomenon, there has been employed a method that the adjusting screw 106 is fixed to the base body 1 by means of adhesive after adjusting the inclination angle by using the adjusting screw 106. However, even when such a method is employed, there may arise a matter that the adhesive is peeled off due to any cause and so the adjusting screw 106 rotates unexpectedly as described above.
In this respect, the aforesaid prior arts 1, 3 and 4 are arranged in a manner that each of the bolt of the prior art 1 and the adjusting screws of the prior arts 3, 4 is applied with a spring pressure thereby to prevent the unexpected rotation of the adjusting screw. However, according to such an arrangement, a coil spring or a leaf spring for generating the spring pressure is additionally required, whereby the number of the parts increases and so the assembling operability is degraded and further the cost increases.